Radiolucent zone of the patella following total knee arthroplasty without patellar resurfacing

Background

The radiolucent zones in the patella are sometimes observed in patients who have undergone total knee arthroplasty (TKA) without patellar resurfacing. On the basis of radiological findings from our clinical experience, we hypothesize that the pathogenesis of this lesion may be similar to that of the lesions of spontaneous osteonecrosis, and this lesion may be due to both osteoporosis and stress concentration. The present study aimed to determine the incidence of the radiolucent zone after TKA without patellar resurfacing. Moreover, the roles of osteoporosis and patellar morphology, which are related to the stress distribution in the patella, were also investigated.

Methods

We studied 48 knees of 38 patients who underwent primary TKA using the Genesis II prosthesis. Axial radiographs taken 1 year postoperatively were used to assess the incidence of the radiolucent zone. The World Health Organization fracture risk assessment tool (FRAX) score and the preoperative patellar facet angle were compared between patients with and without the radiolucent zones.

Results

Five patellae (10.4 %) showed the radiolucent zones postoperatively (the radiolucent group), whereas no such lesions were found in the remaining 43 patellae (the normal group). The major osteoporotic fracture risk of the radiolucent group calculated using the FRAX was 24.8 % and significantly higher than that in the normal group (14.7 %; p = 0.01). The average patellar facet angle in the radiolucent group was 123.6°, which was significantly smaller than that in the normal group (133.6°; p = 0.003).

Discussion and conclusions

The results of the present study suggest that both underlying osteoporosis and a steep patellar facet angle may play an important role in the pathogenesis of the radiolucent zones in patellae after TKA without patellar resurfacing. Patellar resurfacing may be considered, particularly in osteoporotic patients who have a steep patellar facet angle, to avoid the appearance of the postoperative radiolucent zone in the patella.     

The influence of patellar resurfacing on patellar kinetics and retropatellar contact characteristics

Background

Femoropatellar complications are one of the most common problems after total knee arthroplasty (TKA). However, the question of whether to resurface the patella remains controversial. Therefore, we evaluated the kinetics and the retropatellar contact characteristics of patella resurfacing with fixed and gliding surfaces.

Methods

Eight Thiel-embalmed cadaver knees were tested—first intact, then after TKA without patellar resurfacing, and finally with additional patellar resurfacing—while flexing the knee from 0° to 100°. We tested a fixed as well as a gliding patella surface. During the examination, quadriceps and hamstring forces were applied. The retropatellar pressure was determined with a special patella sensor, and the patellar kinetics were measured using an optical three-dimensional motion analysis system.

Results

Resurfacing the patella caused a significant increase in retropatellar pressure and a significant decrease in retropatellar contact area. Using a fixed patella, the retropatellar pressure nearly quadrupled in higher flexion compared to the native patella. Furthermore, the lateral movement of the patella increased after TKA, especially after additional patellar resurfacing.

Conclusions

Resurfacing the patella routinely is not advised. When osteoarthritis of the patella is found, the gliding patella should be preferred.     

Complete excision of the infrapatellar fat pad is associated with patellar tendon shortening after primary total knee arthroplasty

Background

Patella baja is a potentially disabling and difficult-to-treat complication following total knee arthroplasty (TKA). We investigated whether complete or partial excision of the fat pad has an effect on the length of the patellar tendon following TKA.

Methods

A retrospective review of patient radiographs was performed. One hundred and eleven consecutive patients who underwent primary TKA for osteoarthritis using the same components by two consultants were selected. Seventy-two patients underwent complete excision of the fat pad, whilst 39 had partial excision as per consultant practice. Patellar height was measured using the Caton–Deschamps Index (CDI) on immediate postoperative radiographs and at a minimum follow-up of 1 year.

Results

In the complete excision group, the mean CDI changed from 0.54 immediately postoperatively to 0.45 at a minimum follow-up of 1 year (p < 0.0001) indicating shortening of the patellar tendon, and eight patients reported anterior knee pain. The partial excision group’s mean CDI changed from 0.76 to 0.75 (p = 0.231). An analysis of variance showed that the effect of complete fat pad excision on patella tendon length was significant, F(1, 109) = 15.273, p < 0.001.

Conclusion

At a minimum follow-up of 1 year, the patellar tendon length shortened significantly in the group of patients with complete fat pad excision. With partial excision, there was no significant change in tendon length. Complete excision of the fat pad should therefore be avoided wherever possible in an attempt to avoid patella baja.

Level of evidence

II.

     

The effect of femoral component design on patellar tracking in total knee arthroplasty: Genesis II prosthesis versus Vanguard prosthesis

Introduction

The Genesis II knee system incorporates 3° of external rotation into the femoral component and the femoral component is implanted in neutral rotation to the femur. The purpose of this study was to compare patellar tracking of the Genesis II knee system with that of the Vanguard knee system, in which the femoral component is routinely implanted in a 3° externally rotated position to the posterior condylar axis (PCA) of the femur.

Materials and methods

One hundred consecutive knees scheduled to undergo total knee arthroplasty (TKA) were enrolled. Fifty knees underwent TKA with the posterior-stabilized (PS) Genesis II prosthesis and 50 knees underwent TKA with the PS Vanguard prosthesis. Rotation of the femoral component was calculated by measuring the acute angle between the transepicondylar axis (TEA) and the PCA on axial computed tomography (CT) images. The postoperative patellar tilt and displacement were compared between groups. The range of motion and Knee Society scores were also compared.

Results

Forty-eight knees in each group were followed up for 2 years. There was no difference in the angle between the PCA and the TEA on postoperative CT scans between the two designs. There was also no difference in patellar tracking between groups. Both the Genesis II and Vanguard knee systems showed good clinical results at 2 years postoperatively.

Conclusion

The patellar tracking of the Genesis II prosthesis was comparable to that of the Vanguard prosthesis.

Level of evidence

Prospective cohort study, Level II.     

Predictive Factors of “Forgotten Knee” Acquisition After Total Knee Arthroplasty: Long-Term Follow-Up of a Large Prospective Cohort

Background

In a large prospective cohort, we recently showed that only 66.1% of total knee arthroplasty (TKA) with a perfect outcome according to Knee Society Knee Score was completely forgotten in all everyday activities. The main objective of this study was to identify clinical and orthopedic factors associated with the acquisition of “forgotten knee” (FK).

Alteration of the patellar height following total knee arthroplasty

Introduction

Patellofemoral related complications after total knee arthroplasty (TKA) remain clinically relevant. The hypothesis of the present study was that the patellar height changes more than 10 % of its preoperative height after TKA. Possible influences of age, gender, side and navigation system on patellar height were evaluated separately in subgroups.

Materials and methods

A total of 107 knees were enrolled after primary TKA. The patellar height was determined for each patient preoperatively, 1 week and 1 year postoperatively on routinely performed standing lateral view radiographs at 30° knee flexion. Insall–Salvati index (ISI), modified Insall–Salvati index (MIS) as well as Miura–Kawamura index (MKI) were determined for the whole cohort.

Results

One week after TKA the ISI, MIS and MKI changed by more than 10 % in 24 (22 %), 33 (30 %) and 54 (50 %) cases, respectively. Moreover, the 1 year follow-up revealed a decrease or increase of ISI in 30 (28 %), MIS in 47 (44 %) and MK in 65 (61 %) knees. The frequency of patella alta, norma and baja preoperatively as well as 1 week and 1 year postoperatively were not significantly different. Significant differences of patellar height changes were not noted between the defined subgroups.

Conclusions

The present study demonstrates that TKA leads, at 1 week and 1 year follow-up, to patellar height alteration more than 10 % in a significant number of knee joints. However, with the use of ISI and MIS the changes of patellar height did not exceed the defined thresholds to be classified as patella alta or baja.     

Patellar resurfacing versus nonresurfacing in total knee arthroplasty: A meta-analysis of randomised controlled trials

Purpose

Patella resurfacing or nonresurfacing in total knee arthroplasty remains controversial. The aim of this study was to evaluate the efficacy of patellar resurfacing through an evaluation of the current literature.

Methods

We carried out a meta-analysis of randomised controlled trials comparing total knee arthroplasties performed with and without patellar resurfacing. Outcomes of reoperation, anterior knee pain and knee scores were analysed.

Results

Fourteen trials assessing 1,725 knees were eligible. The absolute risk of reoperation was reduced by 4 % (95 % confidence interval, 2–6 %) in the patellar resurfacing arm (between-study heterogeneity, P = 0.05, I² = 42 %), implying that one would have to resurface 25 patellae (95 % confidence interval, 17–50 patellae) in order to prevent one reoperation. There was no difference between the two groups in terms of anterior knee pain, knee pain score, Knee Society score and knee function score. But in the studies followed up for a mean time of not less than five years, a difference was found between the two arms in Knee Society scores (RR = 2.14, 95 % confidence interval, 0.76–3.52; P = 0.002).

Conclusions

The available evidence indicates that patellar resurfacing reduces the risk of reoperation after total knee arthroplasty. Patellar resurfacing patients may make a difference in long-term follow-up (five or more 5 years) of Knee Society scores. In other aspects, the benefit of patellar resurfacing is limited. Additionally, more carefully and scientifically designed randomised controlled trials are required to further prove the claim.     

髌骨钻孔减压改善全膝关节置换术后膝前疼痛

目的探讨通过髌骨钻孔减压术改善全膝关节置换术(TKA)后膝前痛的临床疗效。方法将符合标准的113例行TKA的骨关节炎患者按数字法随机分为两组:54例为减压组,TKA术中联合髌骨钻孔减压术;59例为非减压组,仅施行TKA不联合髌骨钻孔减压术。术后观察两组患者切口愈合情况、相关并发症、KSS评分及膝前痛发生率。结果两组患者切口均一期愈合,无严重并发症发生,113例均获满12个月的完整随访。KSS评分:减压组术后明显高于非减压组;术后膝前痛的发生率明显低于非减压组,差异均有统计学意义(P0.05)。结论 TKA术中联合髌骨减压术可以在一定程度上改善膝关节KSS评分及降低术后膝前疼痛的发生率。     

Effects of local infiltration analgesia for posterior knee pain after total knee arthroplasty: comparison with sciatic nerve block

Background

Although femoral nerve block provides good analgesia after total knee arthroplasty (TKA), residual posterior knee pain may decrease patient satisfaction. We compared the efficacy of periarticular infiltration analgesia (PIA) and sciatic nerve block (SNB) for posterior knee pain.

Methods

Forty-nine patients scheduled for TKA were prospectively randomized into the PIA group (n = 25) or SNB group (n = 24) and received general anesthesia with ultrasound-guided femoral nerve block (FNB). In the PIA group, 60 ml 0.5 % ropivacaine and 0.3 mg epinephrine were injected intraoperatively into the periarticular soft tissue before inserting the components. In the SNB group, patients received ultrasound-guided SNB with 20 ml 0.375 % ropivacaine and periarticular infiltration with 20 ml normal saline and 0.3 mg epinephrine. We evaluated postoperative pain scores, posterior knee pain, frequency of rescue analgesics for 36 h, and performance time of PIA and SNB.

Results

Visual analogue pain scores at 12–24 h were significantly lower in the PIA group than in the SNB group (p < 0.05). The majority of patients had no posterior knee pain. There were no significant differences between the groups in frequency and time of first administration of rescue analgesics and in side effects. Time for performance of periarticular infiltration was significantly shorter than that for SNB (p < 0.05). The dose of intraoperative remifentanil was significantly lower in the SNB group than in the PIA group (p < 0.001).

Conclusions

The combination of FNB and PIA provides sufficient analgesia after TKA. The rapid and convenient periarticular infiltration technique could be a good alternative to SNB.     

The aetiology of total knee arthroplasty failure influences the improvement in knee function

Background

Some indications for revision total knee arthroplasty (TKA), e.g. arthrofibrosis, have been identified to yield inferior results. The aim of this study was to analyse the results of revision TKA according to aetiology of TKA failure.

Patients and methods

The results of 97 consecutive revision TKA in 97 patients stratified according to the aetiology of primary TKA failure (periprosthetic infection, aseptic loosening, instability and arthrofibrosis), were compared using the Knee Society Score (KSS). The effect of patient age, gender, BMI, American Society of Anesthesiologists (ASA) classification, interval to revision and the occurrence of complications on the outcome were also analysed.

Results

After a mean follow-up of 29 months, the KSS had significantly improved in all patient groups (p < 0.001). The analysis of variance among patient groups depicted no significant differences between preoperative KSS (p = 0.618) and postoperative KSS (p = 0.915), while the magnitude of pre- to postoperative improvement showed significant differences between the groups (p = 0.006). The aetiology of primary TKA failure had an independent influence on pre- to postoperative improvement (p = 0.014). Of the other factors analysed, only the ASA classification had an independent impact on postoperative KSS (p = 0.045).

Conclusion

The aetiology of TKA failure has an effect on the improvement in knee function from revision TKA. As no difference was observed between patient groups postoperatively, similar clinical results can be expected independent of the aetiology of primary TKA failure.     

Dynamic in vitro measurement of patellar movement after total knee arthroplasty: an in vitro study

Background  

Changing the kinematic behaviour of patellar movement could be one of the reasons for anterior knee pain after implantation of a total knee arthroplasty (TKA). The aim of the current study was to measure the potential influence on patellar kinematics of patellar resurfacing during TKA.     

Functional versus patient-reported outcome of the bicruciate and the standard condylar-stabilizing total knee arthroplasty

Introduction

The purpose of this retrospective comparative analysis in patients undergoing primary total knee arthroplasty (TKA) was to evaluate whether different TKA implant design would influence patient-rated outcomes, functioning, and range of motion (ROM). A secondary purpose of this study was to test for relationships between the patient-rated outcomes and the passive ROM.

Materials and methods

Thirty-one patients who had a primary bicruciate stabilized TKA performed between May 2010 and November 2012 were retrospectively reviewed and compared with a cohort of 30 patients who had condylar-stabilizing TKA during the same period.

Results

No significant differences were observed between the two groups with respect to preoperative demographic characteristics, ROM and radiographic knee alignment. At a mean follow-up of 37 months (SD 7), the Triathlon group had higher mean Knee Injury and Osteoarthritis Outcome Score (KOOS) score in all subscales and a higher Knee Society Score (KSS) score than the Journey group. This difference was statistically significant for the KOOS subscales of pain (p = 0.0099) and activities of daily living (ADL) (p = 0.0003), as well as the KSS score (p = 0.03846). The ROM was significantly higher in the Journey group when compared to the Triathlon group (p = 0.0013). No significant correlation was observed between the ROM and KOOS pain, QOL and ADL subscores and KSS score.

Conclusions

Postoperative knee ROM and patient perception of knee function after primary TKA can be affected by the different prosthetic designs. However, functionality afforded by the bicruciate TKA is not equivalent to patient satisfaction.

Level of evidence

III.

     

Evidence in orthopaedics: patellar resurfacing in total knee arthroplasty

Abstract Four good quality randomized clinical trials comparing patellar resurfacing versus noresurfacing in knee arthroplasty are analyzed. The outcomes evaluated were anterior knee pain, scores on the Knee Societys rating system and reoperation.No relevant differences were found in knee scores, but anterior knee pain was less frequent in patients with patellar resurfacing. Few patients had severe anterior knee pain. Still, patients with anterior knee pain were less satisfied with the clinical result. Studies with longer follow-up showed that anterior knee pain increased with time in both groups. A clinically relevant increase in reoperation rate in the nonresurfaced group could not be excluded with the numbers available.Anterior knee pain seems to be influenced by the decision of resurfacing the patella during knee arthoplasty. Although it is not associated with important changes in knee scores, patients perceive it as a cause of insatisfaction. Influence of patellar resurfacing on implant supervivence is not clear.     

髌骨软骨破坏程度对保留髌骨的全膝关节置换术疗效的影响

目的 探讨髌骨软骨破坏程度对保留髌骨的全膝关节置换术疗效的影响.方法 2002年1月至2006年5月行全膝关节置换术163例244膝,根据术中观察到的髌骨软骨破坏程度将患者分为轻度、中度、重度软骨破坏三组.所有手术均不置换髌骨.术后随访88例133膝,轻度组42膝,中度组43膝,重度组48膝.采用美国膝关节学会评分(Knee Society Score,KSS)系统(包括膝评分和膝功能评分)和膝前痛评分系统对三组疗效进行评估.结果 随访48～102个月,平均72个月.KSS膝评分和膝功能评分从术前(35.1±5.4)分和(19.2±9.8)分分别提高到(91.7±5.6)分和(83.7±17.5)分.三组KSS膝评分从术前(34.7±6.2)分、(36.5±5.2)分、(35.3±6.2)分分别提高至(92.6±4.5)分、(90.5±6.7)分、(91.9±5.9)分;膝功能评分从术前(14.2±8.6)分、(16.5±7.4)分、(17.0±7.5)分分别提高至(86.6±12.6)分、(82.0±17.2)分、(82.8±21.1)分.三组术后膝评分和膝功能评分的差异均无统计学意义.术后膝前痛的发生率为11.3%(15/133),轻度、中度、重度软骨破坏组分别为11.9%(5/42)、11.6%(5/43)、10.4%(5/48),差异无统计学意义.结论 全膝关节置换术后疗效及膝前痛的发生率与术前髌骨软骨破坏程度无关,髌骨软骨破坏程度不是全膝关节置换术中置换髌骨的可靠依据.

Abstract：

Objective To determine whether there was any correlation between the degree of degenerative changes in the patellar cartilage and the clinical outcome after TKA without patellar resurfacing.Methods A clinical study was performed on 133 knees of 88 patients that underwent TKA without patellar resurfacing from January 2002 to May 2006. According to the degenerative condition of the patellar cartilage,patients was classified as mild group, moderate group, and severe group. Pre- and post-operative evaluations were performed using the knee and function scores of the Knee Society Clinical Rating System (KSS) and Anterior Knee Pain Rating. Results The duration of follow-up was 72 months (range 48-102). The overall knee score of KSS in all patients were improved from 35.1±5.4 preoperatively to 91.7±5.6 postoperatively,and function score of KSS from 19.2±9.8 preoperatively to 83.7±17.5 postoperatively. The mean knee scores of KSS were improved from 34.7±6.2, 36.5±5.2 and 35.3±6.2 preoperatively to 92.6±4.5, 90.5±6.7 and 91.9±5.9 in mild, moderate, and severe group postoperatively, respectively. The mean function scores of KSS were improved from 14.2±8.6, 16.5±7.4 and 17.0±7.5 postoperatively to 86.6±12.6, 82.0±17.2 and 82.8±21.1 in mild, moderate, and severe group postoperatively, respectively. There was no difference among all groups with regard to the postoperative knee scores and function scores of KSS. The prevalence of anterior knee pain was 11.3% in all, and 11.9% in mild group, 11.6% in moderate group and 10.4% in severe group. There was no difference among all groups with regard to the anterior knee pain. Conclusion The clinical outcome and anterior knee pain after TKA without patellar resurfacing was not correlated with the severity of degenerative changes in the patellar cartilage. The degree of degenerative condition of the patellar cartilage is not indication for patellar resurfacing.     

全膝关节置换术中髌骨置换与否对早期疗效及膝前痛的影响

 目的 探讨全膝关节置换术中髌骨置换与否对早期疗效及膝前痛发生率的影响。方法 2010年6月至2011年6月拟行全膝关节置换术患者100例,随机分为两组：髌骨置换组43例50膝,髌骨未置换组57例66膝。比较术后6个月、12个月两组患者的西安大略和麦克马斯特大学(West Ontario and McMaster Universities,WOMAC)骨关节炎指数、美国膝关节外科协会(Knee Surgery Society,KSS)膝评分和功能评分、膝前痛视觉模拟评分(visual analogue scale,VAS)。结果 髌骨置换组与髌骨未置换组患者术后膝前痛VAS评分均较术前明显降低,两组间VAS评分及膝前痛发生率的差异无统计学意义。WOMAC骨关节炎指数6个月分别为28.8±11.2和18.6±7.2、术后12个月分别为20.7±6.2和16.0±5.5,KSS膝评分6个月分别为(87.0±8.3)分和(90.9±7.2)分、术后12个月分别为(84.2±10.6)分和(88.8±9.2)分,KSS功能评分术后6个月分别为(86.6±21.6)分和(84.9±16.5)分、术后12个月分别为(85.2±16.4)分和(91.0±10.0)分,组间差异均无统计学意义。髌骨轴位X线片示髌骨与股骨假体滑车吻合度良好,无不稳及脱位表现。术后1年内无翻修、髌骨表面再置换病例。结论 全膝关节置换术对改善因骨关节炎或类风湿关节炎导致的膝关节疼痛、功能受限有效;髌骨置换与否对术后短期疗效及膝前痛发生率没有影响。     

Arthroscopic transtibial single-bundle posterior cruciate ligament reconstruction using patellar tendon graft compared with hamstring tendon graft

Purpose

The purpose of this study was to compare the outcomes of arthroscopic transtibial single-bundle posterior cruciate ligament reconstruction using autologous patellar tendon and hamstring tendon grafts.

Methods

From 1998 to 2007, 59 patients with symptomatic isolated posterior cruciate ligament injury were included in this retrospective study. Twenty-five knees were reconstructed using bone-patellar tendon-bone graft, and 34 knees were reconstructed using hamstring graft. In both groups, surgical techniques were similar, except material of fixation screws. Patients were evaluated pre-operatively and post-operatively at the latest follow-up with several parameters, including symptoms, physical examination, outcome satisfaction, functional scores, radiography and complications.

Results

Average follow-up period was 51.6 months in patellar tendon group and 51.1 months in hamstring tendon group. Significantly more kneeling pain (32 vs. 3 %), squatting pain (24 vs. 3 %), anterior knee pain (36 vs. 3 %), posterior drawer laxity and osteoarthritic change were shown in patellar tendon group than in hamstring tendon group post-operatively. No significant differences were found in other parameters between both groups.

Conclusions

Several shortcomings, including anterior knee pain, squatting pain, kneeling pain and osteoarthritic change, have to be concerned when using patellar tendon autograft. In conclusion, hamstring tendon autograft may be a better choice for transtibial tunnel PCL reconstruction.     

The effect of trochlea tilting on patellofemoral contact patterns after total knee arthroplasty: an in vitro study

Introduction

Patellofemoral complications are one major concern after total knee arthroplasty (TKA). Anterior knee pain is one of these complications and to a high percentage responsible for unsatisfied patients after TKA. Malrotation of the femoral component can contribute to retropatellar peak pressure and consequently to anterior knee pain.

Materials and methods

Eight fresh frozen cadavers were tested in a force-controlled knee rig after TKA during isokinetic flexing of the knee from 20° to 120° under constant load. By tilting the trochlea in the material of the created femoral component replicas, a rotation of the femoral component by 3° internal, 0° (neutral), 3° and 6° external rotation to transepicondylar line was simulated without changing flexion or extension gap. Retropatellar pressure distribution was measured during flexion and extension of the knee while quadriceps muscles and hamstring forces were applied.

Results

Maximum peak pressure for internal rotation of the trochlea was 7.32 ± 2.31 MPa, in neutral position the pressure reduced slightly to 7.31 ± 2.12 MPa and during further external rotation of trochlea rotation a decrease from 3° with 7.18 ± 2.14 MPa to 6° with 6.22 ± 1.83 MPa was observed (p < 0.01). There was a tendency of lower quadriceps force with increasing external rotation of the trochlea (p = 0.08).

Conclusions

The implantation of the femoral component by 3° internal trochlea rotation to transepicondylar line resulted in a highly significant increase of the mean maximal retropatellar pressure compared to 6° external rotation of the trochlea of the femoral component (p < 0.01). A higher retropatellar pressure might lead to anterior knee pain after TKA. We recommend an external rotation of the femoral component between 3° and 6° to anatomical transepicondylar line to reduce the maximal retropatellar pressure, but only if adequate soft tissue balancing and stable knee kinematics are provided.     

Postural stability in relation to anthropometric and functional characteristics in women with knee osteoarthritis following total knee arthroplasty

Introduction

Due to the controversial information about postural stability in patients with lower limb joints osteoarthritis (OA), the following main questions are raised: how serious is the postural stability disturbance and which factors have an impact on postural stability before and after total knee arthroplasty (TKA).

Materials and methods

Force plate was used to assess postural stability and custom-made dynamometer was used to assess isometric maximal voluntary contraction (MVC) force of leg extensor muscles; besides, knee pain and knee range of motion (ROM) was evaluated in 14 female patients (aged 46–68 years) with knee OA 1 day before, and 3 and 6 months following TKA and once in healthy controls (aged 48–70). Relationship between postural stability during standing and selected anthropometric and functional characteristics were investigated with Spearman’s correlation coefficients.

Results

Remarkable reduction of knee pain and improvement in active ROM for the operated leg were shown after unilateral TKA. MVC force of leg extensor muscles achieved the preoperative level half a year after TKA. The centre of pressure (COP) of sway displacement in anterioposterior (AP) and mediolateral direction and the equivalent area of COP sway for the operated leg did not differ before, 3 and 6 months after TKA and compared to the non-operated leg. The trace speed was 6 months after TKA equal to the preoperative level. Only the COP of sway displacement in AP direction is significantly greater in knee OA patients both before and after TKA compared with healthy controls.

Conclusions

Knee OA patients’ postural stability characteristics did not differ significantly both before and after TKA. Compared to healthy controls, the COP of sway displacement in AP direction is mostly disturbed. Correlation analysis confirms that increased postural sway is associated with an increased equivalent area of COP. In knee OA patients higher body mass index ensures reduced trace speed and lower knee ROM.

Level of evidence

Prospective comparative study, Level II.     

Knee strength retention and analgesia with continuous perineural fentanyl infusion after total knee replacement: randomized controlled trial

Purpose

Despite providing adequate pain relief, a femoral nerve block can induce postoperative muscle weakness after total knee arthoplasty (TKA). Fentanyl has been shown to have peripheral effects but has not been used as a perineural infusate alone after TKA.

Methods

Sixty patients scheduled for TKA were randomized to one of three blinded groups: a continuous 24 h infusion of either fentanyl 3 μg/ml, ropivacaine 0.1 %, or 0.9 % normal saline through a femoral nerve sheath catheter at 10 ml/h. The main outcome was maximum voluntary isometric contraction (MVIC) in the quadriceps femoris (knee extension), measured by a handheld dynamometer (Nm/kg). Other variables assessed were preoperative and postoperative visual analog scale (VAS) scores, hamstrings MVIC (knee flexion), active range of motion of the operative knee, distance ambulated, incidence of knee buckling, supplemental morphine usage, postoperative side effects, and serum fentanyl levels.

Results

Quadriceps MVIC values were significantly greater in the fentanyl group compared to the group that received ropivacaine (median values, 0.08 vs. 0.03 Nm/kg; p = 0.028). The incidence of postoperative knee buckling upon ambulation was higher in the ropivacaine group compared to the fentanyl group, although not statistically significant (40 % vs. 15 %, respectively; p = 0.077). VAS scores while ambulating were not significantly different between the fentanyl group and the ropivacaine group (p = 0.270). Postoperative morphine consumption, nausea and vomiting, and resting VAS scores were similar among the three groups.

Conclusions

A continuous perineural infusion of fentanyl produced greater strength retention than ropivacaine post-TKA.